Primates Have Been Observed to Make Different Calls in the Presence

Primates have been observed to make different calls in the presence of various other species. This is because

A) they are trying to attract some species, but repel others.
B) each call is designed to scare each kind of predator away most effectively.
C) different species that may attack the primates have different abilities to hear the primate calls.
D) they want to warn members of their groups of specific kinds of predators, in order to elicit a correct response.